Integrated power stage device with offset monitor current for sensing a switch node output current

ABSTRACT

An integrated power stage device includes a switch node that is coupled to an output inductor. The integrated power stage device generates a monitor current that is a scaled version of the current through the output inductor. The integrated power stage device outputs a single-ended offset monitor current that is equal to the monitor current plus a DC offset current. A PWM controller senses the current through the output inductor by receiving a monitor voltage that is developed from the offset monitor current. The PWM controller generates a PWM signal in accordance with the sensed output inductor current to control a switching operation of a power switch of the integrated power stage device.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/110,200, filed on Jan. 30, 2015, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to electrical circuits, and moreparticularly but not exclusively to power supplies.

2. Description of the Background Art

Power supply circuits, such as DC-DC converters, can include a powerswitch and an output inductor. The power switch can be a metal oxidesemiconductor field effect transistor (MOSFET), for example. Theswitching operation of the power switch is controlled, e.g., bypulse-width modulation (PWM), to maintain a regulated output voltage.The power switch can be used in conjunction with a synchronous diode orsynchronously with another power switch.

An integrated power stage device includes the power switch and a powerswitch driver in the same chip, i.e., in the same integrated circuit(IC) package. Example integrated power stage devices include the SmartPower Stage™ (SPS) devices from Fairchild Semiconductor and DrMOS(integrated driver-MOSFET) devices. An integrated power stage devicedoes not have an integrated switch controller, and is thus typicallyemployed in conjunction with a separate switch controller, such as a PWMcontroller IC. The PWM controller controls the switching operation ofthe power switch based on the current through the output inductor.

SUMMARY

In one embodiment, an integrated power stage device includes a switchnode that is coupled to an output inductor. The integrated power stagedevice generates a monitor current that is a scaled version of thecurrent through the output inductor. The integrated power stage deviceoutputs a single-ended offset monitor current that is equal to themonitor current plus a DC (direct current) offset current. A PWMcontroller senses the current through the output inductor by receiving amonitor voltage that is developed from the offset monitor current. ThePWM controller generates a PWM signal in accordance with the sensedoutput inductor current to control a switching operation of a powerswitch of the integrated power stage device.

These and other features of the present invention will be readilyapparent to persons of ordinary skill in the art upon reading theentirety of this disclosure, which includes the accompanying drawingsand claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an example multi-phase power supplywith output filter DC resistance (DCR) sensing.

FIG. 2 shows a schematic diagram of an example multi-phase power supplywith monitor current sensing.

FIG. 3 shows a schematic diagram of an example integrated power stagedevice that is configured for monitor current sensing.

FIG. 4 shows a schematic diagram of an integrated power stage device inaccordance with an embodiment of the present invention.

FIG. 5 shows further details of the integrated power stage device ofFIG. 4 in accordance with an embodiment of the present invention.

FIG. 6 shows a schematic diagram of a multi-phase power supply inaccordance with an embodiment of the present invention.

The use of the same reference label in different drawings indicates thesame or like components.

DETAILED DESCRIPTION

In the present disclosure, numerous specific details are provided, suchas examples of electrical circuits, components, and methods, to providea thorough understanding of embodiments of the invention. Persons ofordinary skill in the art will recognize, however, that the inventioncan be practiced without one or more of the specific details. In otherinstances, well-known details are not shown or described to avoidobscuring aspects of the invention.

FIG. 1 shows a schematic diagram of an example multi-phase power supply.In the example of FIG. 1, the power supply includes a PWM controller 101and a plurality of integrated power stage devices 102. The power supplyof FIG. 1 is a multi-phase power supply, and includes a separateintegrated power stage device 102 for each output phase.

The PWM controller 101 controls the switching operation of a powerswitch in an integrated power stage device 102 based on the sensedswitch node (see SW pin) output current of that integrated power stagedevice 102. In the example of FIG. 1, the PWM controller 101 includesdifferential current sense input pins (ISENSE+, ISENSE−) for receiving adifferential current signal indicative of the output current at theswitch node. The output current sensing method can be in accordance witha differential current sensing method for sensing the output filter DCresistance, i.e., output inductor DCR.

FIG. 2 shows a schematic diagram of another example multi-phase powersupply. In the example of FIG. 2, the power supply includes a PWMcontroller 201 and a plurality of integrated power stage devices 202.The power supply of FIG. 2 is a multi-phase power supply, and includes aseparate integrated power stage device 202 for each output phase. Thepower supply of FIG. 2 is similar to that of FIG. 1 except for the useof a monitor current (I_(MON)), instead of inductor DCR, to sense outputcurrent at a switch node.

In the example of FIG. 2, an integrated power stage device 202 has anIMON pin for outputting the monitor current I_(MON), which isdifferentially received by the PWM controller 201 on correspondingdifferential current sense input pins. In the example of FIG. 2, the PWMcontroller 201 includes an internal low dropout (LDO) regulator thatgenerates a 1.5V output, which is used in conjunction with the monitorcurrent I_(MON) to form a differential monitor current input to the PWMcontroller 201. In the example of FIG. 2, the monitor current I_(MON) isa single-ended current signal that does not necessarily need a REFINsignal to be input to the integrated power stage device 202.

FIG. 3 shows a schematic diagram of an example integrated power stagedevice 202 that is configured for monitor current sensing. Generallyspeaking, the monitor current I_(MON) is a high bandwidth, real-timesignal that replicates the switch node output current, i.e., the outputinductor current (I_(LOUT)), to the load. The monitor current I_(MON) istypically a scaled version of the output inductor current I_(LOUT). Apredetermined conversion factor C allows for determination of the outputinductor current given the value of the monitor current I_(MON). Theconversion factor C is the gain of the monitor current I_(MON).

A REFIN signal is an external DC signal that is provided by the PWMcontroller to the REFIN pin of the integrated power stage device 202 toestablish a reference voltage for the monitor current I_(MON). The REFINsignal voltage is set to correspond to I_(LOUT)=0 A. The REFIN signalvoltage is regulated within a few percent of accuracy (e.g.,REFIN=1V+/−2%).

The monitor current I_(MON) develops a monitor voltage V_(IMON) on themonitor resistor R_(IMON). The voltage V_(IMON), is indicative of theoutput inductor current I_(OUT). Because the voltage V_(IMON) isreferenced to the REFIN pin of the integrated power stage device 202,the REFIN signal has voltage-range restrictions since the currentmonitor I_(MON) analog circuitry (e.g., amplifiers) in the integratedpower stage device 202 requires headroom to operate properly. Forexample, the REFIN signal can be set by the user to operate between 0.8Vto 2.0V.

Monitor current sensing, i.e., I_(MON) sensing, can be more accuratethan inductor DCR sensing. However, monitor current sensing may requireparticular communication between the PWM controller and the integratedpower stage devices, especially with the IMON and REFIN pins of theintegrated power stage devices. The operating range of the REFIN signalvoltage can be challenging to define and establish and must be setwithin a tight tolerance voltage range. The REFIN pin must also be ableto sink/source current from a corresponding IMON pin. In addition, aREFIN signal must be provided to all integrated power stage devices ofthe multi-phase power supply.

FIG. 4 shows a schematic diagram of an integrated power stage device 303in accordance with an embodiment of the present invention. In theexample of FIG. 4, the integrated power stage device 303 is embodied inan IC package comprising a plurality pins, including a PVCC pin forreceiving a dedicated power source for gate driver output, a VCC pin forreceiving a supply voltage, a VIN pin for receiving an input voltage,BOOT and PHASE pins for receiving a power source for a high side driverthat resides in the boot-phase power domain, an EN pin for receiving anenable signal for enabling/disabling the integrated power stage device303, an SW pin that is connected to the output switch node, a TMON pinfor outputting a temperature monitor signal, and a PWM pin for receivingan external PWM signal for controlling the switching operation of theintegrated power switch of the integrated power stage device 303. In oneembodiment, the integrated power stage device 303 does not include anintegrated PWM controller, and is thus typically employed in conjunctionwith a separate, external PWM controller.

In the example of FIG. 4, the integrated power stage device 303 furtherincludes an IMON* pin that outputs an offset monitor current I_(OFF-MON)that is equal to the monitor current I_(MON) plus a DC offset current.That is, the integrated power stage device 303 offsets the monitorcurrent I_(MON) by a predetermined amount. The IMON pin is labeled as“IMON*” in the example of FIG. 4, i.e., with an asterisk, to indicatethat it outputs an offset monitor current.

In the example of FIG. 4, the IMON* pin is an IMON pin with aninternally generated DC offset added to the monitor current I_(MON).Accordingly, in the example of FIG. 4, the offset monitor currentI_(OFF-MON) is given byI _(OFF-MON) =I _(LOUT) ×C+DC_Offsetwhere, I_(LOUT) is the output inductor current, C is a predeterminedconversion factor, and DC_Offset is a predetermined DC offset. Theoffset monitor current I_(OFF-MON) is thus indicative of the outputcurrent of the integrated switch device 303. As a particular example,the offset monitor current I_(OFF-MON) may be given byI _(OFF-MON) =I _(LOUT)×(5 uA/A)+1 mAwhen the conversion factor is 5 uA/A and the DC offset is 1 mA.Therefore, the output inductor current I_(LOUT) can be determined fromthe offset monitor current I_(OFF-MON) given the conversion factor andthe DC offset. Advantageously, the offset monitor current I_(OFF-MON) isa single-ended signal that can be utilized for sensing the outputinductor current I_(LOUT) at the switch node without requiring anexternal REFIN signal to establish a reference voltage.

In the example of FIG. 4, the offset monitor current I_(OFF-MON)develops a monitor voltage V_(IMON) on the resistor R_(IMON). Becausethe offset monitor current I_(OFF-MON) is the monitor current I_(MON)plus a DC offset, the resistance of R_(IMON) multiplied by the DC offsetgives the value of the voltage V_(IMON) when the monitor current I_(MON)is zero. The resistance of R_(IMON) multiplied by the offset monitorcurrent I_(OFF-MON) also sets the gain for the voltage V_(IMON). The PWMcontroller can thus sense the output inductor current I_(LOUT) from thevoltage V_(IMON).

As particular examples, assuming DC offset=1 mA, conversion factor=5uA/A, R_(IMON)=1 kohm:

-   -   When I_(LOUT)=0 A, I_(OFF-MON)(0 A)=1 mA and V_(IMON(0 A))=1.0V.    -   When I_(LOUT)=20 A, I_(OFF-MON) (20 A)=1 mA+20 A×5 uA/A=1.1 mA        and V_(IMON(0 A))=1.1V.    -   When I_(LOUT)=−20 A, I_(OFF-MON)(−20 A)=1 mA+(−20 A)×5 uA/A=0.9        mA and V_(IMON(0 A))=0.9V.

FIG. 5 shows a schematic diagram of an integrated power stage device 303in accordance with an embodiment of the present invention. In theexample of FIG. 5, the power stage device 303 includes an integratedpower switch 501 (e.g., N-channel MOSFET), a synchronous switch 502(e.g., N-channel MOSFET), a switch driver 503, a current sense circuit504, and a DC offset generator 505. Other components of the integratedpower stage device 303 are not shown for clarity of illustration.

In the example of FIG. 5, the switch driver 503 receives a PWM signal atthe PWM pin to control the switching operation of the integrated powerswitch 501. The SW pin is connected to the switch node, which in theexample of FIG. 5 is on the source of the integrated power switch 501and the drain of the synchronous switch 502. The integrated power switch501 connects and disconnects the input voltage at the VIN pin to theswitch node in accordance with the PWM signal received at the PWM pin.The current sense circuit 504 senses the output current of theintegrated power stage device 303 at the switch node to generate amonitor current IMON that is indicative of the output current. In theexample of FIG. 5, the DC offset generator 505 comprises a DC currentsource that generates a DC offset current, which is added to the monitorcurrent IMON to generate the offset monitor current I_(OFF-MON) that isoutput at the IMON* pin.

In light of the present disclosure, one of ordinary skill in the artwill appreciate that the integrated power stage device 303 may also beimplemented by making a metal change or other modification to a suitableintegrated power stage device (e.g., Fairchild Semiconductor SPS™device) to add a DC offset current to a monitor current I_(MON) outputat an IMON pin, for example.

FIG. 6 shows a schematic diagram of a multi-phase power supply inaccordance with an embodiment of the present invention. In the exampleof FIG. 6, the power supply includes a PWM controller 201 and aplurality of integrated power stage devices 303, one for each outputphase. Each integrated power stage device 303 provides an offset monitorcurrent I_(OFF-MON) (i.e., I_(OFF-MON1), I_(OFF-MON2), I_(OFF-MON3)) tothe PWM controller 201 to allow the PWM controller 201 to sense itsoutput inductor current I_(LOUT) (i.e., I_(LOUT1), I_(LOUT2),I_(LOUT3)). The PWM controller 201 generates a PWM signal for eachintegrated power stage device 303 according to a corresponding outputinductor current I_(LOUT). In each integrated power stage device 303, aswitch driver drives a power switch in accordance with a PWM signalreceived from the PWM controller 201.

Because an offset monitor current I_(OFF-MON) is single-ended, the PWMcontroller 201 can receive the offset monitor current I_(OFF-MON) on asingle pin, which in the example of FIG. 6 is an ISENSE+pin. Beingsingle-ended, an offset monitor current I_(OFF-MON) is presumed to bereferenced to the signal ground.

In light of the present disclosure, one of ordinary skill in the artwill appreciate that embodiments of the present invention advantageouslysimplify the design of multi-phase power supplies that have integratedpower stage devices. Embodiments of the present invention eliminate theneed for a user-supplied REFIN voltage, which must be well regulated andmust be able to sink/source current. User supplied REFIN voltage mustalso be set to a DC value in accordance with integrated power stagedevice operation range. These limitations make conventional monitorcurrent sensing relatively cumbersome to implement. In marked contrast,in some embodiments of the present invention, a user can simplyimplement a resistor (RIMON) of choice to set the monitor voltageoffset/gain (V_(IMON)=I_(OFF-MON)×R_(IMON)). A suitable PWM controllercan also readily convert the offset monitor current I_(OFF-MON) into avoltage signal. Furthermore, embodiments of the present inventioneliminate the need for differential monitor current sensing for PWMcontrollers.

While specific embodiments of the present invention have been provided,it is to be understood that these embodiments are for illustrationpurposes and not limiting. Many additional embodiments will be apparentto persons of ordinary skill in the art reading this disclosure.

What is claimed is:
 1. A power supply comprising: a first integratedpower stage device comprising a power switch and a switch driver, thefirst integrated power stage device including a switch node that iscoupled to a first output inductor and is configured to output asingle-ended first current that is equal to a second current plus afirst direct current (DC) offset current, the second current being ascaled version of a current through the first output inductor; and apulse-width modulation (PWM) controller that is external to the firstintegrated power stage device, the PWM controller being configured toreceive a first monitor voltage developed from the single-ended firstcurrent to sense the current through the first output inductor and isconfigured to output a first PWM signal to control switching of thepower switch of the first integrated power stage device in accordancewith the current through the first output inductor as indicated by thefirst monitor voltage, wherein the PWM controller is configured toreceive a second monitor voltage developed from a single-ended thirdcurrent that is output by a second integrated power stage device tosense a current through a second output inductor coupled to a switchnode of the second integrated power stage device, and to output a secondPWM signal to control a power switch of the second integrated powerstage device in accordance with the current through the second outputinductor as indicated by the second monitor voltage, wherein the secondintegrated power stage device is external to the PWM controller and thesingle-ended third current is equal to a fourth current plus a second DCoffset current, the fourth current being a scaled version of the currentthrough the second output inductor.
 2. The power supply of claim 1,wherein the power supply is a multi-phase power supply and each of thefirst and second integrated power stage devices corresponds to an outputphase of the multi-phase power supply.
 3. The power supply of claim 1,wherein the first monitor voltage, when the current through the firstoutput inductor is zero, is equal to a product of the first DC offsetcurrent and a resistance of a resistor on which the first monitorvoltage is developed.
 4. The power supply of claim 1, wherein the firstintegrated power stage device further comprises a DC current source thatgenerates the first DC offset current.
 5. A method of operating a powersupply, the method comprising: receiving, in a first integrated powerstage device, a first switch control signal from an external switchcontroller; controlling a switching operation of a power switch of thefirst integrated power stage device in accordance with the first switchcontrol signal; sensing an output current of the first integrated powerstage device to generate a first monitor current that is indicative ofthe output current of the first integrated power stage device; adding aDC offset to the first monitor current to generate a first offsetmonitor current; providing the first offset monitor current to theexternal switch controller; generating, by the external switchcontroller, the first switch control signal based on the output currentof the first integrated power stage device as indicated by the firstoffset monitor current, receiving, in a second integrated power stagedevice, a second switch control signal from the external switchcontroller; controlling a switching operation of a power switch of thesecond integrated power stage device in accordance with the secondswitch control signal; sensing an output current of the secondintegrated power stage device to generate a second monitor current thatis indicative of the output current of the second integrated power stagedevice; adding a DC offset to the second monitor current to generate asecond offset monitor current; providing the second offset monitorcurrent to the external switch controller; and generating, by theexternal switch controller, the second switch control signal based onthe output current of the second integrated power stage device asindicated by the second offset monitor current.
 6. The method of claim5, wherein the external switch controller comprises a pulse widthmodulation (PWM) controller and the first switch control signalcomprises a PWM signal.
 7. The method of claim 5, further comprising:developing a monitor voltage using the first offset monitor current,wherein the external switch controller detects the output current of thefirst integrated power stage device from the monitor voltage.
 8. Themethod of claim 7, wherein the monitor voltage is equal to a product ofthe first offset monitor current and a resistance of a resistor on whichthe monitor voltage is developed when the output current of the firstintegrated power stage device is zero.
 9. The method of claim 5, whereinthe power supply comprises a multi-phase power supply and each of thefirst and second integrated power stage devices outputs a phase of themulti-phase power supply.
 10. The method of claim 5, wherein each of thefirst and second offset monitor currents is a single-ended currentsignal that is referenced to signal ground.
 11. An integrated powerstage device that is an integrated circuit with a plurality of pins, theintegrated power stage device comprising: a first pin in the pluralityof pins, the first pin being configured to receive a switch controlsignal from an external switch controller; a power switch; a switchdriver that is configured to drive the power switch in accordance withthe switch control signal to generate an output current at a switchnode; a second pin in the plurality of pins, the second pin beingconfigured to be is coupled to the switch node; and a third pin in theplurality of pins, the third pin being configured to output an offsetmonitor current, the offset monitor current comprising a DC offset plusa monitor current that is indicative of the output current, the thirdpin being configured to be coupled to one of a plurality of currentsense input pins of the external switch controller.
 12. The integratedpower stage device of claim 11, wherein the external switch controllercomprises a pulse width modulation (PWM) controller, and the first pinis coupled to a PWM signal output of the PWM controller.
 13. Theintegrated power stage device of claim 11, wherein the switch controlsignal is a PWM signal.
 14. The integrated power stage device of claim11, wherein the third pin is coupled to a resistor, the offset monitorcurrent develops a monitor voltage on the resistor, and the switchcontrol signal is generated by the external switch controller based onthe output current as indicated by the monitor voltage.
 15. Theintegrated power stage device of claim 11, further comprising: a DCoffset generator that generates the DC offset.
 16. The integrated powerstage device of claim 15, wherein the DC offset generator comprises a DCcurrent source.
 17. The integrated power stage device of claim 11,further comprising: a fourth pin in the plurality of pins, the fourthpin being configured to receive an input voltage, and wherein the switchnode is on a source of the power switch and a drain of the power switchis connected to the fourth pin.
 18. The integrated power stage device ofclaim 11, wherein the power switch comprises a MOSFET.